67-72 60ft questions
 

I have a lot of questions about what makes a good 60-ft and what I can do to improve mine. My truck is 90% street, but I'm wanting to learn as much as possible.

Current setup:

Engine - 2000 5.3 LS with LS2 takeout cam and Chinese GT45 (69mm) turbo setup
Transmission - TH400 built by me. Summit 3000-stall nitrous converter (anti-balloon plate)
Rear- GM 12-bolt, 3.73's with a spartan locker. stock axles
Front Suspension- Cut coils (approximately 2" drop) KYB monomax shocks
Rear Suspension- Manual bags, poly track bar bushings, KYB monomax
Tires- Cooper Cobra 275/65r15

This is my first track visit after adding the turbo. I was running extremely low boost (5-6psi) for the shakedown runs. I'm in the right lane. launch at the track feels extremely sluggish. absolutely no spin on my tires. The turbo doesn't really spool until about 4000rpm so I have this two second window where it feels like I'm crawling from 3000 to 4000.
http://americanmusc1e.com/Photos/201...456reduced.jpg

Here is the only video we got. It's of a different run where I tried to turn up the boost but I hit the overboost spark cut that I set up in the ecm. https://www.youtube.com/watch?v=TnEl...ature=youtu.be


When the truck was N/A, I had a 2400 stall converter on it that seemed too tight. It wouldn't spin the tires at all on a non-prepped surface. Right before I did the turbo, I added the 3000 stall converter and the truck was much better. I had plenty of wheelspin on the street. Now with the turbo, the converter feels laggy again. i really don't want to go to an even bigger converter because it's primarily driven on the street.

1. Looking through my logs, I can see that the converter is only stalling to about 2500 before trying to push me through the beams. Once I mash the pedal, it flashes to 3000.

2. If I have zero wheelspin with street tires at full pressure, is it worth trying anything with suspension/tires to better my 60-ft or is it all about torque available at launch?

3. Right now my first priority will be getting a real cam. The LS2 cam is proven at the top end, but trades off midrange for similar-sized aftermarket cams.

4. Other than that, I can try switching to a different turbo or tricks to get this one to spool faster.

Re: 67-72 60ft questions
 

Bigger converter and a stickier tire. Perhaps a 2 step to help build boost.

That's where I would start.

Re: 67-72 60ft questions
 

Thats what I was thinking. But I have no turbo experience. I ran a 4500 on the street for years though.

Which ecu are you running? How are you building boost on the line and holding a certain boost level? Do you have a trans brake? That little turbo should come on lightning quick but there is a lot better turbo options depending on your end goal.
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Re: 67-72 60ft questions
 

I'll answer what I can... Haven't done racing in these trucks, but I have in Dodge turbo cars.

If it's hooking good, look at making more power. Once you are making enough power to spin, I would worry about tires and suspension.

I believe you want to focus on the 2500-3000 RPM range. If that cam is going sacrifice power in that range, I don't think it will help the launch.

This 100% is what you need to be concerned with. The turbo should be spooled when you leave the line. It sounds like you are leaving the line, experiencing turbo lag, then the boost hits.

Wondering, depending how you stage if the turbo just doesn't have enough time to spool before launching. I've seen people sit at the line riding the converter for 10+ seconds to build boost for the launch. If your there on a test and tune night, you might want to give it an extra second or 2 to see if you can get that turbo spooled.

Some things that help with lag:
Make sure your waste gate it 100% closed when spooling.
Exhaust is a huge deal. You may benefit from some cutouts as early as possible so the exhaust doesn't have to go through the mufflers.
You can retard the timing while staging to help build boost.
Heat helps your turbo spool. Wrap or coat the exhaust manifolds.

Re: 67-72 60ft questions
 

Wow! thanks for all the responses. I've figured out a few things so far:

1. I missed the fire ring when assembling the wastegate :lol: i've since fixed this. It has definitely helped with spooling the turbo. I start building boost around 3500rpm now and I can hit 5psi between 3800 and 4200 on the street now.

2. I figured out a manual boost control setup and i'm running ~12psi now. This will do nothing for my launch, but it should help on the top end.

3. I switched to a real cam that is known to work well with turbo applications.Sloppy Stage 2. This gave me even more midrange, but I think i my converter may still be too small for the best dragstrip performance. There is still a turbo-less spot for the first 500rpm out of the hole.

4. I've learned a lot about turbos and found out that most single turbo LS guys are using a turbo based on a T4 exhaust housing. My turbo is only 69mm, but it uses the larger T6 housing and fairly heavy internals. This has a lot to do with how slow mine spools up. For around $400 and some exhaust work, I can upgrade to this which should help my spool a lot.

5. I've talked with some guys running T6 turbos and I'm going to add some timing in the <5psi zone to try to get it to spool faster.







I currently have no boost until i'm out of my 60ft. That's why it sucks so bad :waah:

No transbrake. I built the Th400 myself so I could probably figure out how to add one.

The ECM is a Megasqirt MS2 which will do 2-step, but not while controlling a v8. I'd have to step up to a MS3 which is another grand.

currently i haven't seen any boost below 3500. My converter won't budge past 3000. On the street I'll start spinning the rear if I try to hold it with the brakes.

Wrapping the crossover pipe is in the plans for this week. my dipstick tube was leaking and i wanted to fix that first. I don't want oil on my wrap. The manifolds are very thick (cast iron and schedule 40). They should retain heat well.

Out of the turbo I'm 3.5" exhaust dumping just after the cab. The only muffler I have is a 8" glasspack that's 3.5" all the way through.

Re: 67-72 60ft questions
 

A buddy borrowed my chassis that previously had my N20 motor in it.

His old combo was a forfed 6.0 with ported heads and smallish cam with a 76mm turbo. He has a somewhat small converter (3,600 I believe). With a 2 step and a 4L80e he went 1.7x 60's at 12lbs.

In my truck he switched to twins but continued with my 4.22 gear, 32" tall tire and 6,200 rpm converter with my power glide. He went 1.33 60'

Moral of the story.. CONVERTER CONVERTER CONVERTER...

If you can't get to your peak torque instantly, you will never move out as fast as you can.

I am assuming you have a 60e or 80e? If that's the case, don't be affraid of "big" converters as you can lock them for street use.



Advantages are:

Being able to build more RPM while being on the brakes, less likely to push through them.

Quick jump in RPM when you stab it will spool the turbo faster (high exhaust speed)

TQ multiplication will be greater. If the converter has a 2.4 STR, it will effectively multiply TQ at stall rpm by that amount. So if NA you motor makes peak tq at 5,000 rpm due to your cam profile, having a 5,000rpm converter would more like 1,200hp on the hit.


Tune gearing to be +/-200 rpm past peak hours rpm through the traps. Then Convert accordingly.

Re: 67-72 60ft questions
 

Get a transbrake as your next item. Sometime measure the inducer and exducer on your turbo. You may not want to put any $$ into your current turbo depending on what you have exactly. Also depending on what the max power you looking for is a 7675 will come on very quickly and works well on a 5.3 but its a small turbine for a 6.0 and bigger. If you have bigger plans that 850 flywheel I would go T6 Borg Warner 75-80mm with a 96mm turbine. Then on the converter PTC is our normal go to. I just spend a decent chunk of money for ya but you are now into the 9's.